If your EVAP system totally dies on you, you will simply vent gas fumes from the gas tank into the atmosphere directly, instead of filtering them through the charcoal cannister or whatever. And even then, it's a minimal thing. If you parked in a tin shed on a summer afternoon and kept the door closed, you might be sure to put out your cigarette before entering, but otherwise, it's really nothing.

Trust us. Just get used to your new co-driver, man!